Consolidants optimization to reduce proppant embedment in low stiffness carbonate formations

Tight carbonate reservoirs often require specialized stimulation techniques like hydraulic and acid fracturing to enhance production. In soft carbonates, propped fracturing suffers from proppant embedment, and acid fracturing is limited by asperity crushing, channel closure and creeping of the formation, both leading to significant reductions in fracture conductivity. This study demonstrates that treating carbonate rocks with potassium phosphate solutions can significantly increase their hardness. Three potassium phosphate compounds, namely monobasic (KH₂PO₄), dibasic (K₂HPO₄), and tribasic (K₃PO₄), were used to treat Austin chalk and Indiana limestone samples. The reaction between potassium phosphate and calcite generates hydroxyapatite (HAP), which is harder than calcite. The study tested the impact of reaction time and temperature on the stiffness of the rock by employing non-destructive impulse hammering, while the morphology and mineralogy were investigated by X ray Diffraction Analysis (XRD) and Scanning Electron Microscopy (SEM), and elemental composition was evaluated by X ray fluorescence (XRF). The experiment tested 27 reaction scenarios with differing temperatures and aging times. Treatment with 1 M tribasic potassium phosphate resulted in the enhancement of chalk hardness by 221% in the case of 1,000 psi and 70 °C for 72 h. In the case of Indiana limestone, the enhancement was by 122% under similar conditions. Of the three phosphates chemicals, the maximum enhancement of the hardness was shown by tribasic potassium phosphate, followed by dibasic, while the monobasic showed the lowest enhancement Scanning Electron Microscopy and X ray Diffraction analyses revealed differences in hydroxyapatite morphology and quantity under different treatment conditions. The study implies that the treatment by potassium phosphates can reduce the conductivity loss of the fractures in carbonate reservoirs, providing an alternative solution to enhance well productivity.